1. Field of the Invention
The present invention relates to cellular telephone communication systems, and more particularly to a system and method that provides for enhanced transparent call delivery to roaming subscribers of cellular telephone services and the interoperability of differing call delivery systems and communications among mobile telephone switching offices.
2. Description of the Prior Art
Cellular telephone service is widely available, and the operational capabilities of the systems, switching equipment and computer software utilized to provide cellular telephone service are well known and documented. The product literature of companies selling cellular switches and cellular software is readily available and contains full descriptions of the equipment and software capabilities available today. U.S. Pat. No. 4,901,340, System for the Extended Provision of Cellular Mobile Radiotelephone Service, Parker et al, issued Feb. 13, 1990, discloses a system for call delivery to a cellular telephone service subscriber who has roamed outside the service area of the home cellular system, utilizing a temporary local directory number and a call delivery processor functioning at each mobile telephone switch site. U.S. Pat. No. 5,142,654, Cellular Telephone System And Method For Dynamically Switching Between Call Routing Options, Sonberg et al, issued Aug. 25, 1992, discloses a system and method that provides for dynamic switching between call handling options such as caller notification and call forwarding. U.S. Pat. No. 5,282,240, Apparatus and Method for Directing Calls to Mobile Station Subscribers, Buhl et al, discloses a page first system. U.S. Pat. No. 5,282,250, Method of Carrying Out an Authentication Check Between a Base Station and a Mobile Station in a Mobile Radio System, Dent et al, discloses a pre-call validation system.
The systems for call delivery disclosed in the first two referenced patents are available to cellular telephone systems operators and, through said operators, to cellular subscribers under the trade names and trademarks Follow Me Roaming.RTM., Phone Me Anywhere.RTM., for the system of the Parker et al patent operated by GTE Telecommunications Services Incorporated (GTE TSI), and NationLink.RTM. and RoamAmerica.RTM. for the system of the Sonberg patent operated by Electronic Data Systems (EDS). The Follow Me Roaming.RTM. system is the most widely used and will be designated hereinafter as the FMR system.
Essential to the prior art call delivery systems is that each mobile telephone switching office (MTSO) has its own computer system, or site processor, for setting up fixed delivery of calls to a roaming cellular subscriber. Most of these individual computer systems communicate with a host processor at a clearinghouse operated by GTE EDS.
The Electronic Industries Association (EIA) and the Telecommunications Industry Association (TIA) have published a number of joint standards which pertain to cellular service and which are incorporated herein by reference. EIA/TIA Standard 533, Mobile Station--Land Station Compatibility Specification, applies to the system of this invention. The EIA/TIA Subcommittee TR45.2 has published a series of recommendations entitled Cellular Radiotelecommunications Intersystem Operations, which describe procedures necessary to provide cellular telephone service requiring interaction between different cellular systems and dissimilar switch types. Interim Standard IS-41, Rev. A, (hereinafter "Rev. A"), of said series Cellular Radiotelecommunications Intersystem Operations is currently being implemented at the time of filing of this Application. Further standards (Rev. B and C) have been announced for future implementation. Neither of the prior art call delivery systems conform to IS-41 Rev. A.
The present invention is directed to an enhanced version of the FMR system of Parker et al, hereinafter FMR Plus, whereby not only are the requirements of each increment of IS-41 met as required, but they are met faster and more efficiently utilizing one central computer, or host processor, serving a multiplicity of Mobile Telephone Switching Offices (MTSOs), eliminating the site processors, while having the capability of interoperability with the older FMR system and IS-41 Rev. A systems using X.25 or Signaling System 7 (SS7) transport. FMR Plus implements IS-41 Rev. A automatic roaming, which includes making the identity of the visited system known to the home system (automatic registration), transparent call delivery to the roaming subscriber, and allowing the roamer's service profile features to be changed remotely.
The principal object of the present invention is to provide a cellular call delivery system for automatically delivering calls to roaming cellular subscribers meeting the standards of IS-41 Rev. A while maintaining connectivity with non-IS-41 systems.
It is a further object of the invention to provide an enhanced cellular call delivery system utilizing IS-41 Rev. A with seamless interoperability among Mobile Switching Centers utilizing IS-41 Rev. A via a single switch connection, between MSCs using IS-41 and MSCs which have not implemented IS-41, and the provision of connectivity via the FMR host processor to FMR site processors which reside at cellular switches which have not implemented IS-41, Rev. A.
It is still a further object of this invention to provide an input/output gateway between the FMR host processor and the FMR Plus host processor, enabling message translation between the two systems.
Other objects, features and advantages of the invention will become apparent by reading the enclosed specification with the accompanying drawings.